Coolant Chemistry Control During PWR Shutdown-Cooldown
Because of the current uncertainty and controversy surrounding the biological consequences of exposure to low levels of ionizing radiation, significant efforts are underway to control occupational radiation exposure within the nuclear industry. There is a growing recognition that an important component of these efforts is the work which is aimed at reducing the source of the radiation in those areas of the plant which require inspection, maintenance and repair operations. Decontamination is clearly one approach to source control. Another approach is to control the buildup of radioactive deposits on out-of-core surfaces. For modern pressurized water reactors (PWRs), which operate with very low failed fuel levels, this reduces to controlling the buildup of activated corrosion products. Fortunately, data collected from operating plants indicate that even with present designs and materials better control is possible. For example, some sister plants with nominally similar design show wide variations in their radiation fields, indicating that some plants have, fortuitously, succeeded in controlling the activated corrosion product buildup better than others. This point is illustrated in Figure 1 which shows the trends in the upper sheet contact radiation fields at the three Oconee units. However, despite these clear differences, the identification and development of control techniques are difficult since many of the pertinent phenomena involve a complex interaction of system and operational variables and are, as yet, poorly understood.
KeywordsCorrosion Product Nickel Ferrite Electric Power Research Institute Primary Coolant Solubility Behavior
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